Powder metal mix containing carbonaceous binder and green compacts made therefrom

ABSTRACT

Iron and/or copper powder metal mixes to which about 0.5 percent to about 12 percent coal tar pitch is added can be cold-pressed into green compacts having improved green strength. The green compacts can be sintered and repressed into iron and/or copper powder metal compacts which can contain residual carbon. Iron and/or copper powder metal compacts which contain uncombined carbon and/or combined carbon can be used as wear members and friction lining material in braking devices. The amount of residual carbon in the iron and/or copper powder metal compacts can be increased by substituting graphite or carbon black for a portion of the coal tar pitch added to the iron and/or copper powder metal mixes.

United States Patent [191 Herron et a1.

[ 1 Dec. 10, 1974 POWDER METAL MIX CONTAINING CARBONACEOUS BINDER AND GREEN COMPACTS MADE THEREFROM [75] Inventors: Robert H. Herron; William J.

Smothers, both of Bethlehem, Pa.

[73] Assignee: Bethlehem Steel Corporation,

Bethlehem, Pa.

221 Filed: Feb. 28, 1972 21 Appl. No.: 229,987

[52] US. Cl 106/284, 29/1822, 29/1825, 51/305, 51/309, 106/36, 106/38.28, 106/280, 106/281, 75/.5 BA, 75/05 R [51] Int. CL. C08h 13/00, C08h 17/12, C08h 17/08 [58] Field of Search 106/38.9, 36, 280, 281, 106/284, 56, 38.25, 38.28, 38.8; 29/1822,

182.5; 75/.5 BA, .5 R

OTHER PUBLICATIONS Abraham, Asphalts and Allied Substances, Sixth Ed., Vol. II, D. Van Nostrand Co., Inc., NY. TN853 A35 1960 C2. pages 94-101, relied on, Properties of Coal-Tar Pitches.

Primary ExaminerJoseph L. Schofer Assistant ExaminerI-lerbert J. Lilling Attorney, Agent, or Firm-Joseph J. OKeefe; Charles A. Wilkinson; John S. Simitz [57] ABSTRACT Iron and/or copper powder metal mixes to which about 0.5 percent to about 12 percent coal tar pitch is added can be cold-pressed into green compacts having improved green strength. The green compacts can be sintered and repressed into iron and/or copper powder metal compacts which can contain residual carbon.

Iron and/or copper powder metal compacts which contain uncombined carbon and/or combined carbon can be used as wear members and friction lining material in braking devices. The amount of residual carbon in the iron and/or copper powder metal compacts can be increased by substituting graphite or carbon black for a portion of the coal tar pitch added to the iron and/or copper powder metal mixes.

23 Claims, 8 Drawing Figures PATENTEL 3.853.572 SHEET 2 [1F 4 CALCINED KYANITE METAL MATRIX CARBON PAIENIEU 3.853.572

sum 3 or 4 CALCINED up KYANITE METAL mmx GRAPHITE COMMERCIAL COMPOSITION CONTAINING GRAPHITE FIG. 5

RELATIONSHIP OF CARBON BLACK CONTENT ON REDUCTION IN STRENGTHS OF COMPACTS OB% TOTAL PITCH PLUS CARBON BLACK x IO TOTAL PITCH PLUS CARBON BLACK REDUCTION INS ENGTH-% 0 0| 5 a '8 8 8 0 IO 20 3O 4O 5O 6O 7O 8O CARBON BLACK REPLACING PITCH FIG. 6

POWDER METAL M lX CONTAINING CARBONACEOUS BINDER AND GREEN COMPACTS MADE THEREFROM BACKGROUND OF THE INVENTION This invention is directed to iron and/or copper powder mixes to which a carbonaceous binder has been added, the coldpressed green compacts formed therefrom, and iron and/or copper powder metal compacts formed by sintering and re-pressing the green compacts. The iron and/or copper powder metal compacts can contain residual carbon combined and/or uncombined.

Powder metal mixes usually contain a binder such as zinc stearate. The binder aids in providing strength for the green compacts formed by cold pressing whereby the green compacts can be handled prior to sintering to produce the final powder metal compact.

The graphite is added as a source of carbon which, in the case of an iron powder compact, can combine with the iron to form steel. Such compacts are stronger and more wear resistant than iron compacts which do. not contain carbon and have the added advantage that they are heat treatable. In the case of friction materials, the graphite can be added in amounts sufficient to add carbon in uncombined form to aid in reducing wear during service.

The carbon added in prior art practices is in the form of discrete particles of well crystallized graphite derived from carbon graphitized at elevated temperatures or from natural flake graphite. The carbon particles are irregular in shape and have low density. As a result, blending of the powder metal mixes to obtain .a uniform distribution of the carbon is extremely difficult. Segregation of the carbon in the powder metal mixes occurs. Then, too, little or no bonding occurs between the carbon particles or between the carbon particles and the powder metal particles. The carbon particles also prevent metal to metal contact between the powder metal particles thereby weakening the green compacts formed by cold-pressing the mixes. The carbon also weakens the sintered product and can lead to excessive non-uniform wear rates in the finished friction article.

Prior powder metal compacts, such as inorganic friction articles of the type used as lining material for disc brakes on aircraft and high speed automotive vehicles or heavy duty automotive vehicles, and off-the-road trucks, military vehicles and the like, comprise a sintered metal matrix and frictionmodifying and wearmodifying addition agents, which enhance friction properties and wear properties thereof, and graphite. As exemplified in U.S. Pat. No. 2,784,105 issued Mar. 5, 1957 to F. E. Stedman et al and U.S. Pat. No. 3,019,514 issued Feb. 6, 1962 to Roy E. Bickelhaupt et al, carbon, in the form'of graphite, is incorporated into the sintered metal liner to minimize torque buildup during friction engagement and to prevent welding and seizing of opposed surfaces.

Recently, the concept of friction pairs, wherein dissimilar metallic members are formed by powder metal techniques and are used as rubbing surfaces, has been developed. However, the problems inherent in the early devices are also present in friction pairs.

It is an object of this invention to provide an iron and- /or copper powder metal mix which contains a carbonaceous material as a binder.

naceous material as a precursor of a carbon residue in the powder metal compact formed therefrom.

It is an object of this invention to provide an iron and- /or copper powder metal mix which contains coal tar pitch.

It is an object of this invention to provide an iron and- /or copper powder metal mix which contains coal tar pitch and which can be processed by powder metallurgy techniques into wear members and friction lining materials in braking devices.

It is an object of this invention to provide a method for producing iron and/or copper powder metal compacts from iron or copper powder metal mixes containing coal tar pitch.

It is an object of this invention to provide a method for producing iron and/or copper powder metal compacts from iron and copper powder metal mixes containing coal tar pitch wherein said iron and copper metal mixes and coal tar pitch are blended at a temperature for a time to obtain a uniform mix.

It is an object of this invention to provide an iron powder mix containing coal tar pitch as a fugitive binder, said mix being formed into powder metal compacts by powder metal techniques.

It is an object of this invention to provide an iron powder mix containing coal tar pitch as a binder, said mix being cold pressed into green compacts having improved green strength.

lt is an object of this invention to provide an iron and- /or copper powder metal mix containing coal tar pitch as a binder and a precursor of carbon, which carbon is formed by pyrolysis of the coal tar pitch during sintering of the green compact. The carbon can be in the form of combined carbon, uncombined carbon or a mixture of combined and uncombined carbon.

It is an object of this invention to provide an iron powder metal mix containing coal tar pitch as a binder and a precursor of carbon, which carbon, formed by pyrolysis of the coal tar pitch during sintering of the green compacts, is fine grained, poorly crystallized and uniformly distributed throughout the powder metal compact.

It is an object of this invention to provide an iron powder mix containing friction-modifying agents and- /or wear-modifying agents and coal tar pitch as a binder and a precursor of carbon, said mix being processed by powder metal techniques into powder metal compacts usable as friction lining material or wearing surfaces in friction devices.

lt is an object of this invention to provide a copper powder mix containing friction-modifying agents and- /or wear-modifying agents and coal tar pitch as a precursor of carbon, which carbon is formed by pyrolysis during sintering of the green compacts and is fine grained, poorly crystallized and uniformly distributed throughout the sintered powder metal compact.

It is an object of this invention to provide a powder metal mix containing friction-modifying agents and wear-modifying agents and coal tar pitch as a precursor of carbon wherein a portion of the coal tar pitch is replaced by additions of graphite and/or carbon black.

It is an object of this invention to provide a powder metal compact consisting of an iron matrix, frictionmodifying and/or wear-modifying agents and a carbon residue which is fine grained and poorly crystallized and is uniformly distributed throughout the iron powder compact.

It is an object of this invention to provide an iron powder compact having improved green strength formed by powder metal techniques, said iron powder compact substantially devoid of carbon.

It is an object of this invention to provide an iron powder compact which can be used as a wear member and/or a friction lining material in braking devices containing a carbon residue of fine-grained poorly crystallized carbon uniformly distributed throughout the powder metal compact.

It is an object of this invention to provide a copper powder compact formed by powder metal techniques, said copper powder compact containing frictionmodifying agents and wear-modifying agents and a carbon residue of fine-grained poorly crystallized carbon uniformly distributed throughout the powder metal compact, said powder metal compact being useful as a friction lining material or a wear surface in braking de vices.

SUMMARY OF THE INVENTION Broadly, this invention is directed to an iron and/r copper powder metal mix containing a coal tar pitch binder, a green compact formed therefrom and a powder metal compact processed therefrom by powder metal techniques. More specifically this invention is directed to an iron and/or copper powder mix containing coal tar pitch as a binder and/or as a precursor of carbon residue, optionally friction-modifying agents and- /or wear-modifying agents, green compacts having improved green strength formed by cold pressing the mix and powder metal compacts formed by sintering the green compacts. A portion of the coal tar pitch can be replaced by additions of graphite or carbon black. The powder metal compacts can be used as friction material and/or wear surfaces in friction devices.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a graph comparing the green strength of cold pressed iron powder mixes to which coal tar pitch has been added as a binder and an iron powder mix to which graphite and zinc stearate have been added as a binder.

FIG.. 2 is a graph showing the effect of the sintering atmosphere on the amount of residual carbon which remains in the powder metal compact after sintering.

FIG. 5 is a reproduction of a photomicrograph taken at a magnification of 80 diameters of a cross-section of a prior art powder metal friction article containing residual carbon which had been added to the powder metal mix in the form of graphite.

FIG. 6 is a graph showing the effect of substituting carbon black for a portion of coal tar pitch as an additive to a powder metal mix on the strength of the sintered compact.

FIG. 7 is a graph showing the relationship between coal tar pitch added to a copper powder mix and the porosity and strength of the sintered compact.

FIG. 8 is a graph showing the relationship between coal tar pitch added to an iron powder mix and the porosity of the sintered compact.

DESCRIPTION OF THE PREFERRED EMBODIMENT Iron and/or copper powder metal mixes which contain a carbonaceous addition agent as a fugitive binder or as a binder and a precursor of a carbon residue in either a combined and/or uncombined state, can be cold pressed into green compacts having improved green strength. The green compacts can be processed by automatic equipment without failing due to spalling, splitting and the like. Iron and/or copper powder metal compacts processed by powder metallurgy techniques, that is, sintering and repressing, from the green compacts can be used in non-friction devices and as wear members and/or as friction lining material in braking devices. The iron and/or copper powder metal compacts can be processed to remove substantially all the carbonaceous addition agent or to retain a portion of the carbon formed by pyrolysis of the carbonaceous addition agent during sintering. The residual carbon can be in combined form and/or uncombined form.

The carbonaceous addition agent can be coal tar pitch, petroleum tar pitch and the like and should have a relatively low softening point temperature. Carbonaceous addition agents with a low softening point temperature minimize the temperature used during blending of the mixes, are volatilized at low temperatures, yield a relatively large amount of residual carbon upon coking and have a minimum amount of impurities, for example, sulfur and the like. It is preferred to use coal tar pitch having properties listed below in Table 1:

Table 1 Properties of Preferred Coal Tar Pitches Property Test Method Ranges Softening Point (*C) ASTM Dbl-68 (Below 80 C) ASTM D-23Ig-66 (Above 80 C) -]20 Ouinoline Insoluble ASTM D-23l866 2-20 Coking Value-Conradson 70) ASTM D-24l668 30-60 The amount and type of coal tar pitch which is added to the iron and/or copper powder metal mixes is dependent upon the powder metal mix and the end use of the powder metal compact which is produced. To illustrate the above, the range of parameters are listed below in Table 2:

Iron powder metal compacts substantially completely free of residual carbon or containing up to about 8 percent combined and/or uncombined residual carbon and copper powder metal compacts containing about 8 percent uncombined residual carbon can be produced from the iron and/or copper powder metal mixes of the invention. The amount of residual carbon which is found in the iron and/or copper powder metal compacts of the invention is dependent upon the amount and type of coal tar pitch which is added to the iron and/or copper powder metal mixes of the invention, the atmosphere present in the furnace during sintering and the time and temperature of sintering.

Turning now to iron powder metal mixes to which coal tar pitch is added, if an iron powder metal compact substantially completely free of residual carbon is desired as in case No. I, Table 2, then about 0.5 percent to about 2.0 percent coal tar pitch is added to the iron powder metal mix. Although coal tar pitches having a softening point within temperature ranges of 55 to 120 C can be added, it is preferred to add coal tar pitches having a softening point within the temperature range of about 55 to about 100 C. The green compacts are sintered at a temperature above about l,800 F for a time in a hydrogen-rich atmosphere. If an iron powder metal compact, having residual carbon in combined form, as iron carbide as in case No. 2, Table 2, is desired, then about 2 to about 4 percent coal tar pitch having a softening point of about 55 C to about 100 C is added to the iron powder metal mix. The green compact is sintered at a temperature of above about 1,800 F for a time in an atmosphere containing low hydrogen and can contain some nitrogen. In both of the above cases 1 and 2 the iron powder metal can have a particle size which can be coarse, 40 mesh, or can be medium, 100 mesh, and the coal tar pitch is added as a binder to add strength to the green compacts formed from the iron powder metal mixes and only incidentally as a precursor of residual carbon.

lron powder metal mixes which are to be processed into iron powder metal compacts suitable for use as awear member in braking devies, case No. 3 in Table 2, have about 4 percent to about 8 percent coal tar pitch having a melting point temperature between about 90 and l C. The green compacts made from the iron powder metal mixes are sintered at a temperature above l,800 F for a time in an atmosphere containing low amounts of hydrogen. The coal tar pitch is pyrolyzed during sintering. A carbon residue which is a finegrained and poorly crystallized network is substantially uniformly distributed throughout the iron powder metal compact. About 2 to 3 percent of the residual carbon is uncombined and about 0.5 percent to about 1.0 percent residual carbon is combined in the form of iron carbide. In order to increase the wear resistance characteristics and friction characteristics of the iron powder metal wear member, wear inhibitors, such as silicon carbide and the like, and friction-modifying agents, such as mullite and the like, can be added to the iron powder metal mixes. The iron powder metal mixes can be about percent to about 95 percent iron, the remainder the above mentioned wear inhibitors, friction-modifying agents and alloying agents such as molybdenum, titanium, etc. in the iron powder. The iron powder metal particle size can be about l00 mesh sieve size.

Iron powder metal mixes, which are to be processed into iron powder metal compacts to be used as friction lining materials in braking devices, case No. 4a in Table 2, have about 4 percent to about 10 percent coal tar pitch having a softening point temperature between about and 120 C. The green compacts coldpressed from the iron powder metal mixes are sintered at a temperature above about l,800 F for a time in an exothermic or endothermic atmosphere substantially completely free of hydrogen, one such atmosphere being cracked methane. The coal tar pitch is pyrolyzed during sintering. A carbon residue is formed, which is a fine-grained and poorly crystallized network substantially uniformly distributed throughout the iron powder metal compact. About 2 percent to about 5 percent of the residual carbon is in the form of uncombined carbon. Of course, the residual carbon can be as much as 8 percent if graphite or carbon black is also added to the iron powder metal mix.

Friction-modifying agents, such as mullite, low melting point metals, deoxidizing agents are added to the iron powder metal mix. Of course, the iron powder can contain alloying elements such as nickel and molybdenum and the like. Therefore, the iron powder metal mix is about 70 percent to about percent iron. The iron powder metal particles can be about -l00 mesh to about -200 mesh sieve size. The iron powder metal compacts disclosed in cases No. 3 and No. 4a can be used as friction pairs in braking devices for automotive vehicles, in aircraft, off the road equipment, and the like.

Referring to case No. 4b in Table 2, copper powder metal mixes which are to be processed into copper powder metal compacts suitable for use as friction lining material have about 4 percent to about 12 percent coal tar pitch having a softening point of about 90 to about added thereto. Coal tar pitches having lower and higher softening point temperatures can be used to make the copper metal powder mixes and compacts, however, for best results the aforementioned 4 percent to 12 percent range is preferred. The green compacts cold-pressed from the copper powder metal mixes are sintered at about 1,800 F for a time in an exothermic or endothermic atmosphere substantially completely free of hydrogen. The coal tar pitch is pyrolyzed during sintering of the green compact. The copper powder metal compact contains about 2 percent to about 8 percent residual carbon in uncombined form. The residual carbon is a fine-grained, poorly crystallized network substantially completely uniformly distributed throughout the copper metal powder compact. As is well known in the art, friction-modifying agents such as calcined kyanite, mullite, sillimanite, wollastonite, spodumene, silica and the like, deoxidizing agents, low melting point metals can be added to the copper powder metal mixes. The copper powder metal mixes can be about 60 percent to about 90 percent copper. The copper powder metal can have a particle size of 200 mesh sieve size.

Carbonaceous materials, such as graphite and carbon black, can be substituted for a portion of the coal tar pitch to increase the amount of residual carbon in the iron and/or copper powder metal compacts of the invention. Unexpectedly, the substitution of graphite or carbon black does not adversely affect the green strength of green compacts formed from the iron and- /or copper powder metal mixes of the invention.

The effect of coal tar pitch and coal tar pitch with graphite on the green strength of green compacts is graphically illustrated in FIG. 1.

An iron powder metal Containing 98.2 percent iron and the remainder incidental impurities associated with hydrogen reduced sponge iron and 90 percent of the particles passing a 100 mesh sieve size, was divided into four equal portions. One portion was mixed with 2 percent coal tar pitch, a second portion was mixed with 6 percent coal tar pitch, a third portion was mixed with 1.0 percent coal tar pitch and 0.7 percent graphite and the fourth portion was mixed with 1.1 percent graphite and 0.75 percent zinc stearate to duplicate prior art practices. The coal tar pitch added to the iron powder metal mix portions 1 arid 2 had a softening point of 112 C, a quinoline insoluble percent of 11.7 and a Conradson-coking value percent of 56.7. The third ing temperature. lron powder metal compacts which contain either low carbon or high carbon contents, said carbon contents being combined and/or uncombined, can be made by controlling the following variables:

1. Amount of coal tar pitch added to form the iron powder metal mix (95 percent to 100 percent iron powder metal),

2. The type of coal tar pitch which is used in the iron powder metal mix based on softening point,

3. The type of atmosphere used during sintering, ei- I ther rich or lean in hydrogen, 4. The sintering temperature, and 5. Time at sintering temperature. Several iron powder metal compacts were made in which the variables were studied. The results of the tests are shown below in Table 3.

Table 3 Variation in Carbon Content of Iron Powder Metal Compacts T.C. Total Carbon C.C. Combincd Carbon 3 U.C. Uncombined Carbon portion was mixed with a coal tar pitch which had a softening point of 94 C, a quinoline insoluble 4.2 percent and a Conradson-coking value of 50.6 percent.

The iron powder metal mixes containing coal tar pitch additions were blended at a temperature of 250 F and the iron powder metal mix containing graphite and zinc stearate was blended at room temperature. The blended portions were coldpressed at the several compacting pressures shown on the graph to form standard green compacts. The green compacts were tested for strength according to ASTM B-378-61T. The first portion is represented by curve A, the second portion by curve B, the third portion by curve C and the prior art portion by curve D shown on the graph. As the compacting pressure increased, the green strength increased as expected. However, the green strength of all the green compacts containing coal tar pitch was greater than the green strength of the prior art green compacts. Unexpectedly, the green strength of the green compact containing a mixture of coal tar pitch and graphite was higher than the green strength of the compacts containing coal tar pitch only at the high compact pressures.

It has been found that the amount of combined residual carbon in an iron powder metal compact is dependent upon the amount of carbon retained in the iron powder metal compact during the early stages of sintering and upon the rate of diffusion of the carbon into the iron, therefore the amount of combined residual carbon is dependent upon the temperature of sintering and the time at sintering temperature. To obtain a large amount of combined carbon, a high sintering temperature and relatively long time at sintering temperature are used. Conversely, large amounts of uncombined carbon are obtained by short holding time at low sinter- As noted above, iron powder metal compacts which are not used 'as friction articles or in friction pairs can be processed with relatively small additions of coal tar pitch, about 0.5 percent to about 4 percent of coal tar pitch, which can have a softening point between 55 C (131 F) and 100 C (248 F). It has been found that the green strength of a powder metal compact made from about percent to about percent iron powder metal to which about 0.5 percent to 2 percent coal tar pitch is added is sufficient to allow automatic handling of the green compact without danger of degradation due to spalling, splitting and the like. It has also been found that larger than normal powder metal compact than heretofore possible can be produced on existing equipment by incorporating the coal tar pitch in the iron powder metal mix in the amounts mentioned above. Coarse, "40 mesh size, and medium, ---1 00 mesh size powder metals can be processed by powder metal techniques into powder metal compacts having substantially no carbon residue. I

Pyrolysis of the coal tar pitch during sintering leaves a substantially continuous network of fine poorly crystallized carbon residue uniformly distributed throughout the article. The amount of the carbon retained in the sintered part is about 2 to 5 percent, dependent upon the atmosphere used in sintering and the amount of coal tar pitch added to the powder metal mix.

As noted in Table 2, a portion of the carbon added to the powder metal mix can be in the form of carbon black or graphite. The power metal friction article produced from the powder metal mix has higher friction coefficients, low wear rates and higher strength than prior art friction articles.

As shown in Table 2, the green compacts can be sintered in an atmosphere containing hydrogen to produce the powder metal compacts of the invention. The atmosphere can be substantially pure hydrogen or have a ratio of three parts of hydrogen to one part of nitrogen or can contain low hydrogen. The powder metal wear member is sintered in an atmosphere containing low hydrogen and the iron and copper powder metal friction lining material is sintered in an atmosphere which is substantially free of hydrogen, such as exothermic or endothermic cracked methane. The effect of hydrogen in the atmosphere on the amount of retained carbon in the powder metal compact after sintering is shown in FIG. 2. FIG. 2 is a graph showing the effect of sintering at l,000 C of green compacts at various atmospheres. The compacts were made from a powder metal mix consisting of iron powder and 6 percent of a coal tar pitch having a softening point of 1 12 C. Note that in an atmosphere of 100 percent hydrogen, the sintered article contained 1.17 percent carbon, in an atmosphere of 75 percent hydrogen and 25 percent nitrogen, the sintered article contained 1.7 percent carbon and in an atmosphere of 100 percent nitrogen the sintered article contained 3.1 percent carbon.

During the early stages of heating in the sintering process, in the mixes containing more than about 4 percent pitch, the pitch remelts and forms a continuous liquid phase which is held within the article by capillary forces so that a dual continuous structure of liquid pitch and a metal network is formed. As the sintering process continues, metal particles are sintered by solid state diffusion, while the continuous liquid pitch phase is pyrolyzed into a continuous carbon network in which the carbon crystallites, formed by the elevated sintering temperature, have bonded together.

The well dispersed carbon network does not detract from the strength of the friction article and can add to the strength provided by the sintered metal.

The carbon resulting from the pyrolysis of pitch comprises a poorly crystalline carbon having an ultrafine crystallite size of the order of I ,u. The physical nature and distribution of the carbon in the friction article of this invention is quite different from the wellcrystallized graphite particles of prior friction compositions. Graphite particle size in prior art friction articles ranges from about p. to 200 .1..

In addition to the continuous carbon distribution developed by a pyrolyzed coal tar pitch in the structure of a friction article, it has been found that there is no noticeable bloating of the friction article during sintering of a pitch-blended composition. Bloating, and consequent weakening of the physical structure of the friction composition, frequently developed when graphite was used as the carbon source.

To illustrate the continuity of the network of carbon remaining in the article resulting from the above treatment, reference is made to FIG. 3. FIG. 3 is a photomicrograph of a cross section of a sintered powder metal article having a copper metal matrix, and calcined kyanite, made at a magnification of 80 diameters. The carbon in the composition in FIG. 3, represents pitch residual, all organic volatile material in the pitch having been removed from the composition by pyrolysis during sintering. The carbon distribution is shown in FIG. 4, which is the area encompassed in the dotted lines of FIG. 3. FIG. 4 was taken at a magnification of 450 diameters. Note that the carbon is fine and substantially continuous.

FIG. 5 is a photomicrograph taken at a magnification of diameters of a prior friction article containing copper, kyanite and graphite. It will be observed that the carbon represented by the graphite is not of a con tinuous nature. It is this lack of continuity and the large size of the graphite crystals which render graphitecontaining compositions more friable and less wear resistant than compositions of this invention.

Graphite and/or carbon black can be substituted for a portion of the coal tar pitch in the binder metal mix to increase the amount of carbon network residue in the powder metal compact after sintering.

As noted in FIG. 6, the substitution of carbon black for a portion of coal tar pitch in copper powdercalcined kyanite-coal tar pitch mixes does not significantly adversely affect the compressive strength of sintered friction articles made therefrom. We have found that a substitution of up to about 60 percent carbon black for coal tar pitch can be made before the compressive strength of the final product is affected,

Carbon black is a quite compatible addition to the carbon derived from pyrolyzed pitch, as the carbon black crystallites (particles size less than about 0.3 ,u) are consistent with the particle size of the pitchproduced carbon. Any commercial carbon black, produced from natural gas, petroleum or other sources, is acceptable. We have used a thermal black, grade Sterling MT of the Cabot Corp. which has a particle size of 0.250 microns which is the arithmetic mean as measured from electron micrographs, a volatile content of 0.5 percent calculated as the loss in weight when heated to 950 C in a neutral atmosphere and an ash content of 0.75 percent when tested by ignition. Other carbon blacks, channel blacks and furnace blacks are usable if the particle size is smaller than about 0.250 microns and the fixed carbon [100 minus (the percent volatiles the percent ash content)] is not less than about percent. Of course economic considerations will also be used as a guide in the selectiono of the carbon black which is used.

Graphite can also be added to powder metal mixes containing coal tar pitch to obtain improved pressed density, increase the residual carbon after sintering or to obtain specific friction properties. When graphite is added to increase pressed density or increase residual carbon content, the graphite should be a highly crystalline synthetic or natural flake graphite with a fine particle size (at least 95 percent minus 325 mesh). Coarse particle size graphite powder can be added to powder metal mixes containing coal tar pitch to obtain compacts having specific friction properties.

To evaluate the effect of varying additions of coal tar pitch to conventional powder copper and iron mixes which are processed by standard cold pressing, sintering and repressing powder metal techniques, several test samples were made. The results of the tests on the samples are shown in FIGS. 7 and 8. FIG. 7 is a graphite of tests performed on standard copper powder mixes which have calcined kyanite added thereto.

As noted in FIG. 7, the apparent porosity of sintered friction article, to which 2 percent pitch has been added, is about 21 percent. As the amount of pitch in the mix is increased up to 10 percent the apparent porosity decreased to about 16 percent. Further additions up to l6 percent pitch resulted in an increase in the apparent porosity to about 22 percent. The compressive strength of the sintered friction article increased from about 13.6 X 10 pounds per square inch with 2.0 percent pitch addition to a maximum of 18.6 X 10 pounds per square inch with a 10 percent addition of pitch. 1ncreasing the amount of pitch resulted in a decrease in the crushing strength to about 11 X 10 pounds per square inch with a 16 percent addition of pitch.

Since about 50 percent of coal tar pitch is lost as volatiles during Sintering, higher additions of coal tar pitch should result in higher porosity of the sintered friction article. However, as shown in FIG. 7, we have found that the apparent porosity, line A, of the sintered friction article decreased up to additions of about 9 percent to 10 percent coal tar pitch and then did actually increase. It is postulated that the addition of coal tar pitch enhances the pressing characteristics of the metal powder-refractory material mix so that the sintered friction article actually has less pores. Note that the theoretical pressed density, line B, increases at a steady rate up to additions of about 8 percent coal tar pitch and there is a less rapid increase at greater additions. The decrease in porosity is probably due to the fact that the decrease in pores due to pressing offsets the pores formed by pyrolysis of the pitch. Although we have postulated the cause of low porosity when high porosity can be expected, we do not wish to be held to this theory. As can be expected, the compressive strength, line C, generally varies inversely with the porosity of the sintered friction article.

FIG. 8 is a graph showing the sintered porosity and pressed theoretical density of compacts made from standard powdered iron mixes to which coal tar pitch was added.

Generally, the pressed theoretical density and sintered porosity of the parts made from iron powder coal tar pitch mixes followed the same trend as the sintered friction article made from copper powder-calcined kyanite-coal tar pitch mixes. However, the sintered porosity of the iron powder-coal tar pitch mixes increased to very high values at pitch contents of more than about 10 percent. In iron powder mixes the pitch content should not exceed 10 percent. lf higher residual carbon contents in the sintered article are desired than can be obtained by pyrolysis of 10 percent pitch then carbon black and/or graphite should be added to the mix in addition to the pitch.

in order to evaluate the copper powder metal compact used as a friction lining of this invention under simulated operating conditions, a comparative dynamometer test was made to determine friction and wear. In the test, Sample A comprised a brake liner composition containing carbon from pyrolyzed pitch, while Sample B comprised a composition containing the graphite of prior practice. Test specimens were formulated with the following ingredients:

Sample A 1. copper powder 80% 2. calcined kyanite 20% 3. pitch 8% 4. carbon black 2% Sample B l. copper powder l .5% 2. calcined kyanite l2.0% 3. graphite l 3 .5% [plus other ingredients]: Fe

Mo 5% BaSO 1.5% Sb 1.5% Ni 5.0%

Test specimens for Samples A and B were formed by mixing proportionate amounts of the components of an individual specimen. Sample A was then heated to about 350 F while Sample B was not heated. The Sample A was blended in a muller type (Simpson) blender and blended at 300350 F for 20 minutes. Sample B was blended at room temperature in a conical type blender. After blending, the batch was cooled to room temperature and granulated through a 20 mesh screen to break up any lumps. The thus-prepared material was pressed (compacted) into a 2% inch diameter retaining cup at a pressure of 40,000 psi. The cup, made from 1050 steel, had a wall thickness of 0.050 inch. After compacting, the combined cup and specimen lining thickness was Va inch. The article was next sintered in a muffle furnace packed with coke breeze. Sintering temperature was l,800 F for a soak period of 2 hours. The heating rate was about 400 F per hour. After sintering and cooling, the article was repressed (densified) at 100,000 psi. Completed test specimens were riveted to the smooth face of a stator, and the specimen surfaces ground flat. 12 specimens of a single sample spaced equidistant from each other were applied to the stator for testing an alloy steel rotor (Timken alloy No. 6302).

Dynamometer operating test conditions for the test are shown below in Table 4.

' Energy total energy absorbed by the brake/total lining surface area Speed surface speed at the lining at the beginning of the stop 1 KE kinetic energy fiNE normal energy or the norm-.11 landing conditions of a fully loaded aircraft #RTO rcjccied take-off Dynamometer test results for Test 1 are given below in Table 5.

Table 5 Character of Test Test 1 Sample A Sample B 60% KB (break-in)l0 stops Friction coefficient 0.404 0.299 Weight Loss (|b./s/s)** Stator (test specimen) 0.00163 0.00196 Rotor 0.00045 0.00078 60% KE Taxi 21 stops Friction coefficient 0.368 0.313 Weight Loss Stator 0.00160 0.00472 Rotor +0.00007 0.00092 NE 12 stops Friction coefficient 0.292 0.194 Weight Loss Stator 0.00356 0.00495 Rotor 0.00092 0.00253 RTO Friction coefficient 0.139 0.124 Weight Loss Lining 0.0939 0.0625 Rotor +0.0025 Stop Time (seconds) 17.5 21.3

' tangential force/normal lond p011ndslsnrfucclstop All percentages given herein and in the appended claims are by weight.

In a specific example of the invention, a hydrogen reduced sponge iron powder, which analyzed 98.2 percent iron and the remainder incidental impurities usually associated with this type of iron powder, was blended with coal tar pitch constituting 3 percent of the mix and carbon black constituting 3 percent of the mix in a blender for about 5 minutes at a temperature of 250 F. The coal tar pitch had a softening point of 1 12 C, a quinoline insoluble of 11.7 percent and a coking value Conradson of 56.7 percent. The mix was allowed to cool. Several test specimens were then coldcompacted at a compacting pressure of 40,000 pounds per square-inch. Several of the green compacts were tested according to ASTM B-378-61T. The green strength was 960 pounds per square inch. The remaining specimens were placed in a furnace preheated at 500 F and sintered at 2,000 F for 2 hours in an atmosphere having a 3:1 ratio of hydrogen to nitrogen. The specimens were cooled at room temperature in a cooling zone of the furnace. The specimens were tested according to ASTM E8-61T. The tensile strength was found to be 20,600 pounds per square inch and the elongation 1.5 percent. The residue carbon was found to be 3.3 percent as free carbon and 0.9 percent as combined carbon. Specimens were coined at 100,000 pounds per square inch. The tensile strength of the coined compacts was 28,3000 pounds per square inch and the elongation 2.5 percent. The retained carbon was well distributed throughout the specimen and was found to have a crystalline size of about 1.5 .1..

In another specific example of the invention an iron powder prepared by an atomization process and containing substantially 100 percent iron and mixed with 6 percent coal tar pitch and no carbon black was processed and tested as in the first specific example. The strength of the green compacts was 1,300 pounds per square inch. The tensile strength after sintering was 16,500 pounds per square inch and the elongation was 1.5 percent. After coining 100,000 pounds per square inch, the tensile strength was 20,800 pounds per square inch and the elongation was 1.5 percent.

In another specific example of the invention an iron powder metal mix, substantially 98.2 percent iron and incidental impurities, was mixed with 1.0 percent coal tar pitch having a softening point of 94 C determined by ASTM A2319, a quinoline insoluble of4.2 percent determined by ASTM D2318 and a Conradson coking value of 50.6 percent determined by ASTM D2416 and 0.7 percent graphite. The mixture was blended at about 120 C. The blended mix was cold-pressed into green compact test specimens at 40,000 pounds per square inch. The green density was 5.87 grams per cubic centimeter, the green strength was l,500 pounds per square inch. The green compact was sintered at 2,050 F for 45 minutes in a 3 to 1 hydrogen to nitrogen atmosphere. The sintered tensile strength was 22,700 pounds per square inch and the elongation was 3.0 percent.

We claim:

1. A powder metal mix suitable for processing into both a green compact characterized by improved green strength and a sintered powder metal compact, said powder metal mix consisting of about 99.5 percent to about 90 percent of an iron powder metal mix, said iron powder mix consisting of about 70 percent to about 95 percent iron powder and the remainder at least one addition agent taken from the group consisting of silicon carbide, mullite, carbon black, graphite, nickel, molybdenum and titanium, and about 0.5 percent to about 10 percent of at least one carbonaceous addition agent taken from the group consisting of coal tar pitch and petroleum tar pitch, which carbonaceous addition agent has a softening temperature between about 55 C. to about 120 C., a quinoline insoluble percent of about 2 to about 20 and a coking value-Conradson percent of about 30 to about 60, said carbonaceous addition agent being a fugitive binder in the green compact when present in amounts of about 0.5 percent to about 4 percent and a precursor of carbon remaining in the sintered powder metal compact made therefrom when present in amounts of about 4 percent to about 10 percent.

2. The powder metal mix of claim 1 consisting of about 92 percent to about 96 percent iron powder and about 4 percent to about 8 percent coal tar pitch characterized by having a softening temperature within the range of about C. to about 120 C., said coal tar pitch being a precursor of carbon formed by pyrolysis of the coal tar pitch during sintering of the green compact to form the sintered powder metal compact, said carbon being a fine-grained, poorly crystallized network uniformly distributed in the sintered powder metal compact.

3. The powder metal mix of claim 1 consisting of about 90 percent to about 96 percent of said iron powder metal mix and about 4 percent to about 10 percent coal tar pitch characterized by having a softening temperature within the range of about 90 C. to about 120 C., said coal tar pitch being a precursor of carbon formed by pyrolysis of the coal tar pitch during sintering of the green compact to form the sintered powder metal compact, said carbon being a fine-grained, poorly crystallized network uniformly distributed in the sintered powder metal compact.

4. The powder metal mix of claim 1 wherein about 20 percent to about 60 percent of the carbonaceous addition agent is replaced by at least one carbon material taken from the group consisting of graphite and carbon black, said carbon black being characterized by having a particle size less than 0.3 microns and a fixed carbon of not less than about 95 percent.

5. A powder metal mix suitable for processing into both a green compact characterized by improved green strength and a sintered powder metal compact, said powder metal mix consisting of about 98 percent to about 99.5 percent iron powder and about 0.5 percent to about 2.0 percent coal tar pitch characterized by having a softening temperature within the range of about 55 C. to about C., a quinoline insoluble percent of about 2 to about 20 and a coking value- Conradson percent of about 30 to about 60, said coal tar pitch being a fugitive binder in the green compact formed therefrom.

6. A powder metal mix suitable for processing into both a green compact characterized by improved green strength and a sintered powder metal compact, said powder metal mix consisting of about 96 percent to about 98 percent iron powder and about 2.0 percent to about 4.0 percent coal tar pitch characterized by having a softening temperature within the range of about 55 C. to about 100 C., a quinoline insoluble percent of about 2 to about 20 and a coking value -Conradson percent of about 30 to about 60, said coal tar pitch being a fugitive binder in the green compact formed therefrom. I

7. A powder metal mix suitable for processing into both a green compact and a sintered powder metal compact, said powder metal mix consisting of about 88 percent to about 96 percent copper powder and about 4 percent to about 12 percent of at least one carbonaceous addition agent taken from the group consisting of coal tar pitch and petroleum tar pitch characterized by having a softening temperature within the range of about 90 C. to about 120 C., a quinoline insoluble percent of about 2 to about 20 and a coking value- Conradson percent of about 30 to about 60, said carbonaceous addition agent being a precursor of a carbon residue in the sintered powder metal compact formed by pyrolysis of the carbonaceous addition agent during sintering of the green compact to form the sintered powder metal compact.

8. An iron powder metal green compact characterized by having improved green strength and suitable for processing by sintering to produce a sintered iron powder metal compact, said green compact consisting of about 99.5 percent to about 90 percent'iron powder metal mix, said iron powder metal mix consisting of about 70 percent to about 95 percent iron powder and the remainder at least one addition agent taken from the group consisting of silicon carbide, muliite, carbon black, graphite, nickel, molybdenum and titanium and about 0.5 percent to about 10.0 percent of at least one carbonaceous addition agent taken from the group consisting of coal tar pitch and petroleum tar pitch having a softening temperature between about 55 C. to about 120 C., a qunioline insoluble percent of about 2 to about 20 and a coking value-Conradson percent of about 30 to about 60, said carbonaceous addition agent being a fugitive binder in said green compact when present in amounts of about 0.5 percent to about 4 percent and a precursor of carbon in the sintered compact produced therefrom when present in amounts of about 4 percent to about percent in said green compact.

9. The iron powder metal green compact of claim 8 in which the carbonaceous addition agent is coal tar pitch having a softening temperature between about 55 C. to about 120 C., a quinoline insoluble percent of about 2 to about and a coking value-Conradson percent of about 30 to about 60.

10. The iron powder metal green compact of claim 9 in which about 20 percent to about 60 percent of the coal tar pitch is replaced by graphite.

11. The iron powder metal green compact of claim 8 in which the green strength is about 600 to about 1,000 psi greater than prior art strengths of iron powder metal green compacts.

12. The green iron powder metal compact of claim 9 in which about 20 percent to about 60 percent of the coal tar pitch is replaced by carbon black characterized by having a particle size of less than 0.3 microns and a fixed carbon of not less than about 95 percent.

13. A powder metal mix suitable for processing into both a green compact and a sintered powder metal compact, said powder metal mix consisting of about 96 percent to about 88 percent copper powder metal mix, said copper powder metal mix consisting of about 60 percent to about 90 percent copper powder, and the remainder at least one addition agent taken from the group consisting of calcined kyanite, mullite, sillimanite, wollastonite, spodumene, silica, carbon black, graphite, iron, molybdenum and nickel and about 4 percent to about 12 percent of at least one carbonaceous addition agent taken from the group consisting of coal tar pitch and petroleum tar pitch having a softening temperature between about 55 C. to about 120 C., a quinoline insoluble percent of about 2 to about 20 and a coking value-Conradson percent of about 30 to about 60, said carbonaceous addition agent being a precursor of carbon formed by pyrolysis of said carbonaceous addition agent during sintering of the green compact to form a sintered copper powder compact.

14. A powder metal mix suitable for processing into both a green compact characterized by having improved green strength, and a sintered powder metal compact, said powder metal mix consisting of about 90 percent to about 98 percent iron powder metal mix, said iron powder metal mix consisting of about per-. cent to about 90 percent iron powder and the remainder at least one addition agent taken from the group consisting of silicon carbide, mullite, carbon black, nickel, molybdenum and titanium, and about 2 percent to about 10 percent of a carbonaceous addition agent consisting of about 20 percent to about 60 percent graphite and about percent to about 40 percent coal tar pitch, said coal tar pitch characterized by having a softening temperature within the range of about 55 C. to about 120 C., a quinoline insoluble percent of about 2 to about 20 and a coking-Conradson percent of about 30 to about 60, said coal tar pitch being a fugitive binder which is substantially completely dissipated during sintering of the green compact when present in amounts of about 0.5 percent to about 4 percentv and a precursor of carbon in said sintered powder metal compact when present in amounts of about 4 percent to about 8 percent.

15. A powder metal mix suitable for processing into both a green compact characterized by improved green strength and a sintered powder metal compact, of claim 14 wherein said powder metal mix consisting of about percent to about 96 percent iron powder and about 10 percent to about 4 percent of a carbonaceous addition agent consisting of about 20 percent to about 60 percent graphite and about 80 percent to about 40 percent coal tar pitch, said coal tar pitch characterized by having a softening temperature within the range of about 90 C. to about 120 C.

16. A powder metal mix suitable for processing into both a green compact characterized by improved green strength and a sintered powder metal compact, said powder metal mix consisting of about 96 percent to about 98 percent iron powder and about 4 percent to about'2 percent of a carbonaceous addition agent consisting of about 20 percent to about 60 percent graphite and about 80 percent to about 40 percent coal tar pitch, said coal tar pitch characterized by having a softening temperature within the range of about 55 C. to about 100 C., a quinoline insoluble percent of about 2 to about 20 and a cokingvalue-Conradson percent of about 20 to about 60. I

17. A powder metal mix suitable for processing into both a green compact characterized by improved green strength and a sintered powder metal compact, said powder metal mix consisting of about 92 percent to about 96 percent iron powder and about 8 percent to about 120 C., a quinoline insoluble percent of about 2 to about 20 and a coking value-Conradson percent of about 20 to about 60.

18. A powder metal mix suitable for processing into both a green compact characterized by having improved green strength, and a sintered powder metal compact, said powder metal mix consisting of about 90 percent to about 98 percent iron powder metal mix, said iron powder metal mix consisting of about 70 percent to about 90 percent iron powder and the remainder at at least one addition agent taken from the group consisting of silicon carbide, mullite, graphite, nickel, molybdenum and titanium, and about percent to about 2 percent of a carbonaceous addition agent consisting of about percent to about 60 percent carbon black and about 80 percent to about 40 percent coal tar pitch, said carbon black characterized by having a particle size of less than 0.3 microns and a fixed carbon of not less than 95 percent and said coal, tar pitch characterized by having a softening temperature within the range of about 55 C. to about 120 C., a quinoline insoluble percent of about 2 to about 20 and a coking- Conradson percent of about to about 60, said coal tar'pitc'h being a fugitive binder in said green compact when present in amounts of about 0.5 percent to about 4 percent and a precursor of carbon remaining in the sintered powder metal compact when present in amounts of about 4 percent to about 8 percent in the green compact.

19. A powder metal mix suitable for processing into both a green compact characterized by having improved green strength and a sintered powder metal compact, said powder metal mix consisting of about 96 percent to about 98 percent iron powder and about 4 percent to about 2 percent of a carbonaceous addition agent consisting of about 20 percent to about 60 percent carbon black and about 80 percent to about 40 percent coal tar pitch, said carbon black characterized by having a particle size of less than 0.3 microns and a fixed carbon of not less than 98 percent and said coal tar pitch characterized by having a softening tempera ture within the range of about 55 C. to about 100 C., a quinoline insoluble percent of about 2 to about 20 and a coking-Conradson percent of about 30 to about 60.

20. A powder metal mix suitable for processing into both a green compact characterized by having improved green strength and a sintered powder metal compact, said powder metal mix consisting of about 92 percent to about 96 percent iron powder and about 8 percent to about 4 percent of a carbonaceous addition agent consisting of about 20 percent to about 60 percent carbon black and about 80 percent to about 40 percent coal tar pitch, said carbon black characterized by having a particle size of less than 0.3 microns and a fixed carbon of not less than 95 percent and said coal tar pitch characterized by having a softening temperature within the range of about 90 C. to about 120 C., a quinoline insoluble percent of about 2 to about 20 and a coking-Conradson percent of about 30 to about 60.

21. A powder metal mix suitable for processing into both a green compact characterized by having improved green strength and a sintered powder metal compact, said powder metal mix consisting of about 90 percent to about 96 percent iron powder and about 10 percent to about 4 percent of a carbonaceous addition agent consisting of about 20 percent to about percent carbon black and about percent to about 40 coal tar pitch, said carbon black characterized by having a particle size of less than 0.3 microns and a fixed carbon of not less than 95 percent and said coal tar pitch characterized by having a softening temperature within the range of about C. to about 120 C., a quinoline insoluble percent of about 2 to about 20 ant a coking-Conradson percent of about 30 to about 60.

22. A powder metal mix suitable for processing into both a green compact and a sintered powder metal compact, consisting of about 88 percent to about 96 percent copper powder metal mix, said copper powder metal mix being about 60 percent to about 90 percent 7 copper powder and the remainder at least one addition agent taken from the group consisting of calcined kya-,

nite, mullite, sillimanite, wollastonite, spodumene, silica, iron, molybdenum and nickel and about 12 percent to about 4 percent of a carbonaceous addition agent consisting of about 20 percent to about 60 percent carbon black and about 80 percent to about 40 percent coal tar pitch, said carbon black being characterized by having a particle size of less than 0.3 micron and a fixed carbon of not less than percent and said coal tar pitch being characterized by having a softening temperature within the range of about 90 C to about C., a quinoline insoluble percent of about 2 to about 20 and a coking-Conradson percent of about 30 to about 60, said coal tar pitch being a precursor of carbon remaining in the sintered powder metal compact formed by pyrolysis of said coal tar pitch during sintering of the green compact, said carbon being a fine-grained, poorly crystallized network uniformly distributed in the sintered powder metal compact.

23. A powder metal mix suitable for processing into both a green compact and a sintered powder metal compact, said powder metal mix consisting of about 88 percent to about 96 percent copper powder metal mix, said copper powder metal mix being about 60 percent to about 90 percent copper and the remainder at least one agent taken from the group consisting of calcined kyanite, mullite, sillimanite, wollastonite, spodumene, silica, iron, nickel and molybdenum and about 12 percent to about 4 percent of a carbonaceous addition agent consisting of about 20 percent to about 60 percent graphite and about 80 percent to about 40 percent coal tar pitch, said coal tar pitch characterized by having a softening temperature within the range of about 90 C. to about 120 C., a quinoline insoluble percent of about 2 to about 20 and a cokingConradson percent of about 3 to about 60, said coal tar pitch being a precursor of carbon remaining in the sintered powder metal compact formed by pyrolysis of said coal tar pitch during sintering of the green compact, said carbon being a fine-grained, poorly crystallized network uniformly distributred in the sintered powder metal compact. 

1. A POWDER METAL MIX SUITABLE FOR PROCESSING INTO BOTH A GREEN COMPACT CHARACTERIZED BY IMPROVED GREEN STRENGTH AND A SINTERED POWDER MATERIAL COMPACT, SAID POWDER METAL MIX CONSISTING OF ABOUT 99.5 PERCENT TO ABOUT 90 PERCENT OF AN IRON POWDER METAL MIX, SAID IRON POWDER MIX CONSISTING OF ABOUT 70 PERCENT TO ABOUT 95 PERCENT IRON POWDER AND THE REMAINDER AT LEAST ONE ADDITION AGENT TAKEN FROM THE GROUP CONSISTING OF SILICON CARBIDE, MULLITE, CARBON BLACK, GRAPHITE, NICKEL, MOLYBDENUM AND TIATNIUM, AND ABOUT 0.5 PERCENT TO ABOUT 10 PERCENT OF AT LEAST ONE CARBONACEOUS ADDITION AGENT TAKEN FROM THE GROUP CONSISTING OF COAL TAR PITCH AND PETROLEUM TAR PITCH, WHICH CARBONACEOUS ADDITION AGENT HAS A SOFTENING TEMPERATURE BETWEEN ABOUT 55*C. TO ABOUT 120*C, A QUINOLINE INSOLUBLE PERCENT OF ABOUT 2 TO ABOUT 20 AND A COKING VALUE-CONRADSON PERCENT OF ABOUT 30 TO ABOUT 60, SAID CARBONACEOUS ADDITION AGENT BEING A FUGITIVE BINDER IN THE GREEN COMPACT WHEN PERSENT IN AMOUNTS OF ABOUT 0.5 PERCENT TO ABOUT 4 PERCENT AND A PRECURSOR OF CARBON REMAINING IN THE SINTERED POWDER METAL COMPACT MADE THEREFROM WHEN PRESENT IN AMOUNTS OF ABOUT 4 PERCENT TO ABOUT 10 PERCENT.
 2. The powder metal mix of claim 1 consisting of about 92 percent to about 96 percent iron powder and about 4 percent to about 8 percent coal tar pitch characterized by having a softening temperature within the range of about 90* C. to about 120* C., said coal tar pitch being a precursor of carbon formed by pyrolysis of the coal tar pitch during sintering of the green compact to form the sintered powder metal compact, said carbon being a fine-grained, poorly crystallized network uniformly distributed in the sintered powder metal compact.
 3. The powder metal mix of claim 1 consisting of about 90 percent to about 96 percent of said iron powder metal mix and about 4 percent to about 10 percent coal tar pitch characterized by having a softening temperature within the range of about 90* C. to about 120* C., said coal tar pitch being a precursor of carbon formed by pyrolysis of the coal tar pitch during sintering of the green compact to form the sintered powder metal compact, said carbon being a fine-grained, poorly crystallized network uniformly distributed in the sintered powder metal compact.
 4. The powder metal mix of claim 1 wherein about 20 percent to about 60 percent of the carbonaceous addition agent is replaced by at least One carbon material taken from the group consisting of graphite and carbon black, said carbon black being characterized by having a particle size less than 0.3 microns and a fixed carbon of not less than about 95 percent.
 5. A powder metal mix suitable for processing into both a green compact characterized by improved green strength and a sintered powder metal compact, said powder metal mix consisting of about 98 percent to about 99.5 percent iron powder and about 0.5 percent to about 2.0 percent coal tar pitch characterized by having a softening temperature within the range of about 55* C. to about 100* C., a quinoline insoluble percent of about 2 to about 20 and a coking value-Conradson percent of about 30 to about 60, said coal tar pitch being a fugitive binder in the green compact formed therefrom.
 6. A powder metal mix suitable for processing into both a green compact characterized by improved green strength and a sintered powder metal compact, said powder metal mix consisting of about 96 percent to about 98 percent iron powder and about 2.0 percent to about 4.0 percent coal tar pitch characterized by having a softening temperature within the range of about 55* C. to about 100* C., a quinoline insoluble percent of about 2 to about 20 and a coking value -Conradson percent of about 30 to about 60, said coal tar pitch being a fugitive binder in the green compact formed therefrom.
 7. A powder metal mix suitable for processing into both a green compact and a sintered powder metal compact, said powder metal mix consisting of about 88 percent to about 96 percent copper powder and about 4 percent to about 12 percent of at least one carbonaceous addition agent taken from the group consisting of coal tar pitch and petroleum tar pitch characterized by having a softening temperature within the range of about 90* C. to about 120* C., a quinoline insoluble percent of about 2 to about 20 and a coking value-Conradson percent of about 30 to about 60, said carbonaceous addition agent being a precursor of a carbon residue in the sintered powder metal compact formed by pyrolysis of the carbonaceous addition agent during sintering of the green compact to form the sintered powder metal compact.
 8. An iron powder metal green compact characterized by having improved green strength and suitable for processing by sintering to produce a sintered iron powder metal compact, said green compact consisting of about 99.5 percent to about 90 percent iron powder metal mix, said iron powder metal mix consisting of about 70 percent to about 95 percent iron powder and the remainder at least one addition agent taken from the group consisting of silicon carbide, mullite, carbon black, graphite, nickel, molybdenum and titanium and about 0.5 percent to about 10.0 percent of at least one carbonaceous addition agent taken from the group consisting of coal tar pitch and petroleum tar pitch having a softening temperature between about 55* C. to about 120* C., a qunioline insoluble percent of about 2 to about 20 and a coking value-Conradson percent of about 30 to about 60, said carbonaceous addition agent being a fugitive binder in said green compact when present in amounts of about 0.5 percent to about 4 percent and a precursor of carbon in the sintered compact produced therefrom when present in amounts of about 4 percent to about 10 percent in said green compact.
 9. The iron powder metal green compact of claim 8 in which the carbonaceous addition agent is coal tar pitch having a softening temperature between about 55* C. to about 120* C., a quinoline insoluble percent of about 2 to about 20 and a coking value-ConraDson percent of about 30 to about
 60. 10. The iron powder metal green compact of claim 9 in which about 20 percent to about 60 percent of the coal tar pitch is replaced by graphite.
 11. The iron powder metal green compact of claim 8 in which the green strength is about 600 to about 1,000 psi greater than prior art strengths of iron powder metal green compacts.
 12. The green iron powder metal compact of claim 9 in which about 20 percent to about 60 percent of the coal tar pitch is replaced by carbon black characterized by having a particle size of less than 0.3 microns and a fixed carbon of not less than about 95 percent.
 13. A powder metal mix suitable for processing into both a green compact and a sintered powder metal compact, said powder metal mix consisting of about 96 percent to about 88 percent copper powder metal mix, said copper powder metal mix consisting of about 60 percent to about 90 percent copper powder, and the remainder at least one addition agent taken from the group consisting of calcined kyanite, mullite, sillimanite, wollastonite, spodumene, silica, carbon black, graphite, iron, molybdenum and nickel and about 4 percent to about 12 percent of at least one carbonaceous addition agent taken from the group consisting of coal tar pitch and petroleum tar pitch having a softening temperature between about 55* C. to about 120* C., a quinoline insoluble percent of about 2 to about 20 and a coking value-Conradson percent of about 30 to about 60, said carbonaceous addition agent being a precursor of carbon formed by pyrolysis of said carbonaceous addition agent during sintering of the green compact to form a sintered copper powder compact.
 14. A powder metal mix suitable for processing into both a green compact characterized by having improved green strength, and a sintered powder metal compact, said powder metal mix consisting of about 90 percent to about 98 percent iron powder metal mix, said iron powder metal mix consisting of about 70 percent to about 90 percent iron powder and the remainder at least one addition agent taken from the group consisting of silicon carbide, mullite, carbon black, nickel, molybdenum and titanium, and about 2 percent to about 10 percent of a carbonaceous addition agent consisting of about 20 percent to about 60 percent graphite and about 80 percent to about 40 percent coal tar pitch, said coal tar pitch characterized by having a softening temperature within the range of about 55* C. to about 120* C., a quinoline insoluble percent of about 2 to about 20 and a coking-Conradson percent of about 30 to about 60, said coal tar pitch being a fugitive binder which is substantially completely dissipated during sintering of the green compact when present in amounts of about 0.5 percent to about 4 percent and a precursor of carbon in said sintered powder metal compact when present in amounts of about 4 percent to about 8 percent.
 15. A powder metal mix suitable for processing into both a green compact characterized by improved green strength and a sintered powder metal compact, of claim 14 wherein said powder metal mix consisting of about 90 percent to about 96 percent iron powder and about 10 percent to about 4 percent of a carbonaceous addition agent consisting of about 20 percent to about 60 percent graphite and about 80 percent to about 40 percent coal tar pitch, said coal tar pitch characterized by having a softening temperature within the range of about 90* C. to about 120* C.
 16. A powder metal mix suitable for processing into both a green compact characterized by improved green strength and a sintered powder metal compact, said powder metal mix consisting of about 96 perCent to about 98 percent iron powder and about 4 percent to about 2 percent of a carbonaceous addition agent consisting of about 20 percent to about 60 percent graphite and about 80 percent to about 40 percent coal tar pitch, said coal tar pitch characterized by having a softening temperature within the range of about 55* C. to about 100* C., a quinoline insoluble percent of about 2 to about 20 and a coking value-Conradson percent of about 20 to about
 60. 17. A powder metal mix suitable for processing into both a green compact characterized by improved green strength and a sintered powder metal compact, said powder metal mix consisting of about 92 percent to about 96 percent iron powder and about 8 percent to about 4 percent of a carbonaceous addition agent consisting of about 20 percent to about 60 percent graphite and about 80 percent to about 40 percent coal tar pitch, said coal tar pitch characterized by having a softening temperature within the range of about 90* C. to about 120* C., a quinoline insoluble percent of about 2 to about 20 and a coking value-Conradson percent of about 20 to about
 60. 18. A powder metal mix suitable for processing into both a green compact characterized by having improved green strength, and a sintered powder metal compact, said powder metal mix consisting of about 90 percent to about 98 percent iron powder metal mix, said iron powder metal mix consisting of about 70 percent to about 90 percent iron powder and the remainder at at least one addition agent taken from the group consisting of silicon carbide, mullite, graphite, nickel, molybdenum and titanium, and about 10 percent to about 2 percent of a carbonaceous addition agent consisting of about 20 percent to about 60 percent carbon black and about 80 percent to about 40 percent coal tar pitch, said carbon black characterized by having a particle size of less than 0.3 microns and a fixed carbon of not less than 95 percent and said coal tar pitch characterized by having a softening temperature within the range of about 55* C. to about 120* C., a quinoline insoluble percent of about 2 to about 20 and a coking-Conradson percent of about 30 to about 60, said coal tar pitch being a fugitive binder in said green compact when present in amounts of about 0.5 percent to about 4 percent and a precursor of carbon remaining in the sintered powder metal compact when present in amounts of about 4 percent to about 8 percent in the green compact.
 19. A powder metal mix suitable for processing into both a green compact characterized by having improved green strength and a sintered powder metal compact, said powder metal mix consisting of about 96 percent to about 98 percent iron powder and about 4 percent to about 2 percent of a carbonaceous addition agent consisting of about 20 percent to about 60 percent carbon black and about 80 percent to about 40 percent coal tar pitch, said carbon black characterized by having a particle size of less than 0.3 microns and a fixed carbon of not less than 98 percent and said coal tar pitch characterized by having a softening temperature within the range of about 55* C. to about 100* C., a quinoline insoluble percent of about 2 to about 20 and a coking-Conradson percent of about 30 to about
 60. 20. A powder metal mix suitable for processing into both a green compact characterized by having improved green strength and a sintered powder metal compact, said powder metal mix consisting of about 92 percent to about 96 percent iron powder and about 8 percent to about 4 percent of a carbonaceous addition agent coNsisting of about 20 percent to about 60 percent carbon black and about 80 percent to about 40 percent coal tar pitch, said carbon black characterized by having a particle size of less than 0.3 microns and a fixed carbon of not less than 95 percent and said coal tar pitch characterized by having a softening temperature within the range of about 90* C. to about 120* C., a quinoline insoluble percent of about 2 to about 20 and a coking-Conradson percent of about 30 to about
 60. 21. A powder metal mix suitable for processing into both a green compact characterized by having improved green strength and a sintered powder metal compact, said powder metal mix consisting of about 90 percent to about 96 percent iron powder and about 10 percent to about 4 percent of a carbonaceous addition agent consisting of about 20 percent to about 60 percent carbon black and about 80 percent to about 40 coal tar pitch, said carbon black characterized by having a particle size of less than 0.3 microns and a fixed carbon of not less than 95 percent and said coal tar pitch characterized by having a softening temperature within the range of about 90* C. to about 120* C., a quinoline insoluble percent of about 2 to about 20 and a coking-Conradson percent of about 30 to about
 60. 22. A powder metal mix suitable for processing into both a green compact and a sintered powder metal compact, consisting of about 88 percent to about 96 percent copper powder metal mix, said copper powder metal mix being about 60 percent to about 90 percent copper powder and the remainder at least one addition agent taken from the group consisting of calcined kyanite, mullite, sillimanite, wollastonite, spodumene, silica, iron, molybdenum and nickel and about 12 percent to about 4 percent of a carbonaceous addition agent consisting of about 20 percent to about 60 percent carbon black and about 80 percent to about 40 percent coal tar pitch, said carbon black being characterized by having a particle size of less than 0.3 micron and a fixed carbon of not less than 95 percent and said coal tar pitch being characterized by having a softening temperature within the range of about 90* C. to about 120* C., a quinoline insoluble percent of about 2 to about 20 and a coking-Conradson percent of about 30 to about 60, said coal tar pitch being a precursor of carbon remaining in the sintered powder metal compact formed by pyrolysis of said coal tar pitch during sintering of the green compact, said carbon being a fine-grained, poorly crystallized network uniformly distributed in the sintered powder metal compact.
 23. A powder metal mix suitable for processing into both a green compact and a sintered powder metal compact, said powder metal mix consisting of about 88 percent to about 96 percent copper powder metal mix, said copper powder metal mix being about 60 percent to about 90 percent copper and the remainder at least one agent taken from the group consisting of calcined kyanite, mullite, sillimanite, wollastonite, spodumene, silica, iron, nickel and molybdenum and about 12 percent to about 4 percent of a carbonaceous addition agent consisting of about 20 percent to about 60 percent graphite and about 80 percent to about 40 percent coal tar pitch, said coal tar pitch characterized by having a softening temperature within the range of about 90* C. to about 120* C., a quinoline insoluble percent of about 2 to about 20 and a coking-Conradson percent of about 3 to about 60, said coal tar pitch being a precursor of carbon remaining in the sintered powder metal compact formed by pyrolysis of said coal tar pitch during sinTering of the green compact, said carbon being a fine-grained, poorly crystallized network uniformly distributred in the sintered powder metal compact. 